Scanning system



Oct. 16, 1934. B. UMMINGS, JR 9 9 SCANNING SYSTEM Filed Sept. 15, 1932 INVENTO fi ATTO RNE Patented Oct. 16, 1934 W NITED' S ATES 'PATNT OFFICE Application September 15, 1932, Seral No. 633,289

4 Claims. (Cl.` Iva-e) This invention relates to the electrical transmission of images and more particularly to an improvedmethod and apparatus 'for scanning. The new .method produces superior images at i 5 the receiving Station, in fine detail and improved shading Without any increase in the frequency band Width used for the transmission.

Broadly stated, I scan a picture With a light beam or Virtual light beam, moving this beam first in a series of parallel strokes or approximately parallel to scan the field and then in a second series of parallel strokes not parallel to the first series of strokes to again scan the field.` By repeating this cycle I continually scan the field alternately in non-parallel directionswhich are preferably at right angles to each other. I prefer to use a light beam for scanning Which has a Cross-section rectangular in Shape and travelling in the direction of its shorter dimension. 'The cross-sectional light beam need not be rectangular but I prefer to use a beam of rectangular Crosssection in Which the longer dimension is equal to twice the shorter dimension. A In such a system the Width of the light beam in each stroke is greater than usual for the same requency band Width and hence fewer strokes are required to completely scan the field and consequently the light beam may travel at a slower speed. This slower movement and the relative narrowness of the light beam in the direction of the movement greatly increase the detail While the strokes in the non-parallel direction give greatly increased complementary detail and the superimposed images provide improved detail in all respects.

I find this invention particularly applicable to television where the` image is Viewed directly and I Will so describe it, but it is to be understood that it may be used where the image is to be photographically or otherwise recorded and transmitted at a slower rate.`

By the use of this invention, for a given frequency band Width, the cross-Sectional area of the light beam remains about the same and the number of picture elements actually remains about the same, that is, there are more elements per stroke but less strokes for each scanning; but due to the fact that the rectangular elements intersect, When Superimposed, to form apparent elements of one half the area of the rectangular shape, the number of elements into Which the screen is' actually divided is doubled thus increasing the picture detail.

The scanning is identoal at the transmitter and the receiver, and may be accomplished either by mechanical or electrical means and it is `to be understood that the method described is not limited to any specific apparatus for accomplishing the result although I describe a particular apparatus.

To illustrate the use oI" this invention, assume a Square field being scanned by a light beam having a Square cross-sectional area and in accordance With `the usual method and using a 5 frequency band Width of one hundred kilocycles and scanning at'the rate of twenty times per Second. According to the accepted formula half the product of the number of elements per line times the number of lines times the number o Scannings pe r second equals the requency; hence in this assumed case there Would be one 'hundred lines With one hundred elements per line and there Would be ten` thousand elements. If the` Cross section of the light beam is reduced to seven-tenths its Width in the direction of motion and increased to one andfour-tenths its length in the direction perpendicular to its direction ofmotionthe Cross Sectional area Will remain the same. ,There will be one'hundred 0 and forty `elements per'- line but only seventy lines and scanningat the same rate of twenty times `per second the requency band Width Will be' the same.. Since the beam is narrower the picture detail Will be 'increased in the direction 5 of the scanning motion of the beam. If the field is first Scanned in horizontal strokes and then in Vertical strokes, increased detail Will be obtained in both directions and if the images resulting from scanning in directions perpendicular to each other are ormed alternately and Within a short period of time both images will be retained and superimposed to form a composite picture with greatly improved picture detail. The alternate rectangular elements With 5 their longer aXes perpendicular Will intersect to form apparent elements equal in area to one half of the rectangles, and since in the usual form of scanning the elements are equal in area to the oross-Sectional area of the light beam the result is a picture With twice as many elements and consequently greatly improved cletail. If desired the length of the rectangular Cross-section may be more or less than twice its Width and the Cross-section of the light beam 5 need not be eXactly rectangular and. in scanning With a rotating disk may be formed by two arcs and two radii. V

The invention may be applied in Various ways Without deviating from its principle. One

half revolutions the other disk causes the light' beam to scan the same field with Vertical strokes. The unused part 'of each disk may be, partly cut away so as not to interfere With the operation of the other disk. I have referred to Vertical and horizontal strokes but this is not necessary so long as the field is scanned alternately With strokes travelling in directionsapproximately perpendicular to each other.` By' using three or more disks the picture could be` scanned in three or more directions if desired.

The two disks in the apparatus illustrated are synchronized and rotated at the same speed. If

the disks revolve at ten revolutions per second there' will be twenty scannings of pictures per second, and in one tenth of a second there will be two pictures, one scanned by each disk in lines or strokes perpendicular to each other and due to the retention of the image either by the eye or on a photographic plate they will form, a composite picture' of greatly improved detail without an increase in the frequency band Width, and without a decrease inthe amount of light on the field. l

'In the drawing I have illustrated an arrangement of two scanning disks for scanning according'to my'improved method. In this arrangement va pair of Semi-Circular diskslO and ll' are mounted upon rotatable Shafts 12 and 13 respectively driven by two synchronous motors l l and 15 both revolving at the same' rate of Speed. The disks revolve at the same speed and in the same' relation to' each other. Near the periphery of each of the disks are a number of l approximately rectangular openings 20 the'long er dimension of which extends radially. The

disks are positioned so that the circles described thereby overlap to a considerable. extent and overlap at a point which is 'directly below the shaft 13 and in a horizontal direction from shaft 14-. At this point there is a screen 21 before the disks having an opening 22 therein of Square or rectangular shape, for outlining the field to be scanned. As the openings 20 in the disks pass the opening in the screen a. light Source infront of the screen (not shown) will project the beam through the opening 20 and sweep across the field to be scanned. The 'disks 10 and ll pass alternately behind screen 21 and as they so pass disk 10' is moving upward and'disk 11 moves to the left. Thus disk 10 will scan the field in ve rtical strokes and disk 11 will scan the field in horizontal strokes and the two will scan the field vcontinually and alternately. Qther means may be used for scanning ac- -cordingto'this method. A cathode ray tube may"be used with the proper Circuit or switchmg arrangements Or a single scanning disk may be used with two light sourcesspaced 90 degrees apart behind the disk and focused through the disk upon the same'field.

I claim:

1. A method of scanning which comprises alternately scanning a field with parallel s trokes of a lightbeam and scanning the same field with strokes 'parallel to each other but not to said first mentioned strokes, said scanning being rapid enough so that the eye can retain a complete visual image, and the' light beam having a substantially rectangular Cross section with the Shortest dimension in the direction of the scanning stroke ,2. A method according to claim 1 in which the strokes which are not parallel are at right angles to each other. l

3. A scanning apparatuswhch comprises an apertured disk' arranged to scan a field with parallel strokes, a second apertured disk arranged to scan the same field with parallel strokes not parallel to the -first mentioned strokes, the apertures in said disks being elongated in the direction of the radii of the disks, and means for driving said disks so that they scan the field alternately.

'4. A scanning device'according to claim 3 in which each disk scan in Strokes'which are Substantially at right angles tothose of the other disk.

' BRYAN Y.. CUMMINGS, JR 

